The present invention relates to an apparatus for assisting the starting of a diesel engine employing preheating glow plugs.
It is known to provide preheating plugs in combustion chambers and to heat the preheating plugs until they are red-hot for enhancing the starting of a diesel engine.
In a conventional starting assistance apparatus, a current is passed through the preheating plugs to heat them when a key-operated switch is in an engine starting position. The interval of time before the engine can be started can be reduced by passing a large current through the preheating plugs to make them red-hot at a rapid rate. However, there is a tendency for the heater bodies of the preheating plugs to melt if such a large current is employed, and hence such an arrangement cannot be put to practical use. The prior apparatus, which does not use such a large current, is thus disadvantageous in that it takes about 20 to 30 seconds before preheating can be completed, that is, before the preheating plugs can be heated to a suitable temperature of about 900.degree. C.
Another known apparatus, which is described in West German Offenlegungsschrift No. 1,426,173, includes ignition plugs (preheating plugs) incorporating a heater body having a resistance which increases with rising temperature, with the ignition plugs being connected as resistors in a Wheatstone bridge. When a current passes through the ignition plugs, diametrically opposite terminals of the Wheatstone bridge are brought out of balance. This generates a voltage which is used to cause a control transistor to energize or de-energize a power switch control relay, thereby inserting or shunting a control resistor with the ignition plugs to maintain the ignition plugs at a constant temperature. Such an apparatus includes a device for turning on and off a current through the ignition plugs with a switching element to heat the ignition plugs at a constant temperature. This apparatus is used for ignition plugs for igniting a heater mechanism in a bus having an internal combustion engine, a jet propulsion system using liquid fuel, and the like. Since the ignition plugs are required to be maintained at a constant temperature for a long period of time, the heater bodies must have a resistance large enough for them not to be melted when a rated voltage is continuously applied. Hence, if such ignition plugs are incorporated in a starting assistance apparatus for a diesel engine, they also require 20 to 30 seconds to get the engine started after the key-operated switch has been set in the engine starting position. Thus, such a prior apparatus is advantageous only in applications where the temperature of the ignition plugs is to be maintained constant over a relatively long time period.
It is an object of the present invention to provide an apparatus for assisting the start of a diesel engine substantially immediately upon a key-operated switch being set to an engine starting position.